Tickle is an interesting one. You're working against another Dungeon Keeper who has half-a-clue. He does the Eye of Evil on you (you'll see the circling dots), blasts your imps with lightning, and drops monsters where battles are going on. You're in the bottom-right corner; he's in the top left. Therefore build your standard rooms with your library in the bottom right and your training room as far to the top left as your world will allow.

There's a band of rock and lava across the middle. Be careful when digging the first batch of gold on the left - it leads into lava with some nasty fairies. Wait until you have someone to defend your imps from them. The top of that gold block (on the far left) also opens into a lair of nasties. Then bridge up around that lava to find two gem spots. Don't forget to build a treasure room NEAR them!

There's a room to the far right with a "transfer" gem, two dogs and a spawn. Eventually start heading north towards the other keeper. You'll get into some HUGE battles but if you've been training all along, you shouldn't have too much trouble getting through. You get a temple in this one, so torture your enemies and use the ghosts to fight.

Eventually when you've killed him, go up digging to the very top right. There are three rooms guarded by magical doors. The left and right lead to boulder traps, and a trap guards the room, but through the middle one is a gem which activates a hidden world.